1) Field of the Invention
The invention relates to a thermo-pneumatic actuator comprising a cavity defined by walls and being hermetically sealed, which is inflated with a working medium that alters its gas pressure when a temperature change occurs, wherein a wall region of the cavity is constructed as a ductile membrane, which can be deflected in at least two working positions located on both sides of a neutral position, in which the membrane is curved in opposite directions to one another, and further comprising a tempering device that is heat-conductively connected to the working medium in order to alter the gas pressure in the cavity and to adjust the membrane from one working position to the other working position. The invention further relates to a method for producing a thermo-pneumatic actuator.
2) Discussion of the Prior Art
U.S. Pat. No. 6,149,123 discloses such an actuator. It comprises a substrate plate with a cavity formed in the surface thereof. Arranged on the substrate plate is a cover layer that overlaps the cavity. The cover layer is hermetically sealed with the rim area of the substrate plate surrounding the cavity. The cavity is inflated with a working medium comprising a gas phase, the gas pressure thereof being temperature-dependent. A wall area of the cavity opposite the cover layer is configured as a thin ductile membrane that can be deflected from a neutral position into at least two working positions located on both sides of the neutral position. In a first working position, the membrane is curved away from the cavity so that the volume of the cavity is enlarged relative to the volume wherein the membrane is located in the neutral position. In a second working position, the membrane is curved towards the cavity so that the volume of the cavity is reduced relative to the volume wherein the membrane is located in the neutral position. In order to alter the gas pressure in the cavity and to adjust the membrane from one working position to the other working position, the actuator has a tempering device that is heat-conductively connected to the working medium. The working medium can be heated or cooled by means of the tempering device. The membrane is drive-connected to a valve element moveable between an open position and a closed position, which is arranged in a flow channel and blocks or permits the flow-through of a flow medium located in the flow channel. When the working medium has an over pressure and the membrane is bowed away from the cavity, the valve element is opened. When the pressure in the working medium is the same as the ambient pressure, the membrane is in the neutral position and the valve element is closed. A disadvantage resides in the actuator in that the latter continuously consumes energy in at least one of the two working positions. At certain ambient temperatures it may even become necessary to heat the working medium when the valve element is in the open position and to cool it when the valve element is in the closed position in order to ensure that the valve opens and closes properly. In this case the actuator must be continuously supplied with energy in both working positions of the valve element.
The object of the invention is therefore to create an actuator of the aforesaid type which permits low energy consumption but which can nevertheless be reliably maintained in the respective working position. The object furthermore consists of providing a method for producing such an actuator.